Melanin is a blackish-brown pigment produced by melanocytes present in epidermis, and is an insoluble high molecular weight compound formed by an oxidative condensation reaction by the action of enzymes such as tyrosinase using the amino acid, tyrosine, as a substrate. More specifically, melanin is classified into eumelanin, which exhibits black color, and pheomelanin, which exhibits red color. After being produced by melanocytes, these melanins are transferred in the form of melanin-containing granules (melanosomes) to epidermal keratinocytes present in the periphery thereof, and are excreted from epidermis accompanying turnover thereof. However, as a result of excessive production of melanin by melanocytes that have been activated by such factors as exposure to ultraviolet rays or stress and the subsequent deposition thereof, pigmentation, age spots, freckles or liver spots and the like appear on the skin following sun tanning, thereby becoming a source of concern in terms of aesthetics.
In the past, in addition to cysteine, glutathione and vitamin C, products derived from microorganisms belonging to the genus Trichoderma (Patent Document 1), lactoferrin hydrolysates (Patent Document 2), and amino acid derivatives and peptide derivatives of kojic acid (Patent Document 3) have been reported to have tyrosinase inhibitory action and be able to inhibit the formation of melanin, while specific aromatic compounds such as furanone have been reported to be able to be used as tyrosinase inhibitors and melanin formation inhibitors (Patent Documents 4, 5 and 6).
Moreover, the known α-irone, 4-(2,5,6,6-tetramethyl-cyclohexen-1-yl)-3-buten-2-one (Patent Document 7), γ-irone and precursors of α-irone in the form of iriflorental and iribaridal (Patent Document 8) have been reported to have melanin inhibitory effects.
However, there are cases in which conventionally known melanin formation inhibitors have problems with safety in the manner of hydroquinone, which has recently attracted attention as a skin whitening agent, or the effects thereof may not be adequate in terms of practical use, thereby resulting in a continuing need to search for a novel component having melanin formation inhibitory action.